Ragchew Winter 2019/2020

GB2WFB – WORTHING FIRE BRIGADE SES PETE G0TLU REPORTS ON HIS FIRST VISIT TO THE USA AND THE DAYTON HAMVENTION

Plus JONATHAN G1EXG’S SHORT CIRCUIT PRESIDENTIAL PONDERINGS CHAIRMAN’S CHATTER CORRESPONDENCE BOOK REVIEW RALLIES

Winter 2019/2020

Worthing & District Amateur Radio Club Established 1948 Website: www.wadarc.org.uk

E-mail: info@wadarc.org.uk President: Chris Smith G3UFS WADARC meets every Tuesday at 20.00 in TS Vanguard, 9a Broadwater Road, Worthing BN14 8AD. Anyone who has an interest in radio communications and associated subjects, whether a licensed amateur or not, is welcome to come along.

WADARC can also arrange training courses for the radio amateur Foundation, Intermediate and Advanced licences.

The WADARC Committee 2019 – 2020 Chairman Alan Baker G4GNX Vice-Chairman Ian MacDonald M0IAD Secretary Alex Slee 2E0UMD Treasurer Roger Ferrand G7VBR Alistair Weller M0OAL Norman Jacobs 2E0RKO Vic Benney G8MUQ Kelvan Gale M0KEL Rod Vincent M0RDV These Members have volunteered to accept the following responsibilities: Membership Manager: Ian MacDonald M0IAD Ragchew Editor: Roger Hall G4TNT Website: Alan Baker G4GNX Special Events Stations: Peter Head G4LKW Online Content Coordinator: Alan Baker G4GNX Training Team: Kelvan Gale M0KEL / Rod Vincent M0RDV Press and Publicity Coordinator: Currently Vacant Quartermaster: Bryan Durrant G0SIU Club Calendar Coordinator: Alex Slee 2E0UMD Weekly News Email: Alan Baker G4GNX

WADARC Club Nets (all times are local) 07.30

Sunday

3.725MHz ± QRM SSB

19.30

Monday

145.425MHz (V34/S17)

11.00

Thursday

7.106MHz ± QRM SSB

CONTENTS Editorial .................................................. 4 Presidential Ponderings ......................... 8 Chairman’s Chatter ................................ 10 GB2WFB ................................................ 12 Correspondence ...................................... 14 First Visit to the Dayton Hamvention ....... 20 Short Circuits by Jonathan G1EXG .................... 24 Book Review ........................................... 25 Rallies ..................................................... 26 3

EDITORIAL

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elcome to the Winter 2019/2020 edition of Ragchew. Yes, it has been a while since the last issue and it’s been for the usual reason – a lack of material. I know members don’t want to read a magazine full of just my ramblings so Ragchew has to contain contributions from others. If none come in, we don’t have a magazine.

Fortunately, thanks to a couple of reliable regulars and a newcomer to these pages, I now have enough for another issue – I hope you enjoy it.

Inside This Month In his Presidential Ponderings, Chris G3UFS looks back on the time when he was studying for his amateur licence and recalls having one of those “I wish I’d known that before I …” moments.

In Chairman’s Chatter, Alan G4GNX brings us up to date with happenings at TS Vanguard, including the possible installation of a new radio system that will allow Club members to enjoy out of hours remote radio operation.

In GB2WFB – Worthing Fire Brigade SES, Edmund M0MNG reports on the special event station that was set up at the Worthing Fire Brigade’s Open Day. WADARC regularly attends this is annual event and it not only looks like fun, it’s also a great way of raising the Club’s profile.

In Correspondence, Jonathan G1EXG wrote in with his thoughts on joining metal tubes and whether it is better to fit a square tube into a round one or a round tube into a square one. With the aid of some meticulous mathematics, he’s provided the definitive answer.

In First Visit to the Dayton Hamvention, Pete G0TLU reports on his first time at Dayton and explains that as he thought this might be a once in a lifetime trip, he decided to see as much of America as he could while he was there. He certainly did that! He covered thousands of miles and saw everything from big cities to tiny towns and great lakes to deserts.

This time in his Short Circuits column Jonathan G1EXG looks at variable and vacuum capacitors. He describes the differences between them and explains why you might choose one type in preference to the

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C other when using them in amateur radio applications.

Unusually, we also have a book review in this issue. Jonathan G1EXG has been reading All the Light We Cannot See, a novel by Anthony Doerr. He describes it as a moving and powerful story and it even contains a quote about 80m.

Thank You I really have to give special thanks to the reliable Edmund M0MNG, the prolific Jonathan G1EXG and first-time contributor Pete G0TLU for making this issue possible. If you’ve enjoyed reading their contributions, please let them know.

A Different Type of Ragchew?

Going back to the topic of my opening remarks, producing regular editions of Ragchew is proving to be very difficult because there just isn’t enough material coming in. I’ve chatted to various people about this in the clubroom, trying to define the cause of the problem and to see if we need to change Ragchew to cope with it.

New Sources of Information As I see it (sorry for the clichés), times have changed, technology has moved on and people’s reading habits have changed. There are now many more ways of disseminating information than there were when I was publishing paper magazines and most of them involve the internet.

WADARC has adopted several of them and now, unlike just a few years ago when members had to read a paper version of Ragchew to find out about Club news and events, they now have an abundance of sources.

Website The Club has a very nice website that contains a wealth of information.

It is currently working well but perhaps not at its full potential. That’s for the usual reason – there’s a lot of work involved in keeping it up to date and that work is being carried out by volunteers who are not always able to donate the time needed. It has been suggested it should become the

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C primary source of Club news and that makes sense because nowadays most people who want to find out about something will look for the relevant website. Things proposed for it include videos of outside events and maybe even of guest speakers at the clubroom, propagation articles, contest reports and much more but if that expansion of the site were to happen, the obvious question is – who will do the work? Not just now and then but regularly, week in and week out.

It’s a big task but not impossible – is it something members think the Club should prioritise?

Facebook Similarly, we have a Facebook page that could be used to propagate Club news, videos, event reports and so on. I’ve found many Club members seem to be anti-Facebook but it is very popular and I think it could be a good way for Club members to keep in touch with each other and for the outside world to see what we do and to contact us.

To see the sort of thing a radio club can do with a Facebook page, take a look at the ‘other’ WADARC’s page (just click on this link): https://www.facebook.com/wadarc As you can see, it does pretty much all the things that have been suggested for our website but without the need for someone to devote their time to keeping it up to date – it’s self-populating. The readers provide the content! They can put up articles, videos, photos, they can ask questions and get answers in real time in much the same way we do on the reflector. A bonus is that previous content is fully searchable.

Their page is not perfect but it does show the sort of thing we could be doing if our page was actively supported and promoted.

Do you think the Club should look to improving its presence on Facebook?

YouTube YouTube is a great source of information and Edmund M0MNG is certainly making good use of it. His channel contains lots of excellent videos on amateur radio topics, including special event stations and

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C other events. They’re interesting to watch and often good publicity for the Club. It would be nice to be able to incorporate some of his (and other people’s) relevant videos into our website, Facebook page or an updated version of the newsletter.

Reflector Currently, we are using the reflector as a way of sending out alerts about openings, asking questions, spreading news and so on. It’s just a simple text-based email service but it works and messages are propagated to recipients on the list almost immediately. It’s quick and simple but it does have some disadvantages. To me, the main one is that it’s a closed group so if you’re not on the list, you don’t get to see the messages.

There is one part of this system that is proving to be especially useful.

It’s the weekly newsletter put together by Alan G4GNX. It’s current and it keeps everyone who subscribes to the list up to date with Club news and events. However, for me that’s a two-edged sword. Once a news item has appeared in the newsletter and members have read it, is there any point in me putting it in Ragchew afterwards?

With this in mind, I’ve been wondering if the current version of Ragchew is still the best way of keeping members in touch with the Club.

The weekly newsletter does a great job of providing current news and I’ve been thinking there might be a way of amalgamating it with Ragchew and producing a weekly HTML version of Ragchew that combines the topicality of the newsletter with articles and perhaps even a video or two.

Do you think this is an idea that’s worth pursuing?

Finally If you have any thoughts on the above topics or if there’s something else you’d like to comment on, please do get in touch with me at ragchew@wadarc.org.uk 73, Roger G4TNT

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PRESIDENTIAL PONDERINGS i everyone, it’s that time again, the time when our Editor suggests I probe my memory banks for recollections of my early days in radio, so here goes.

I’ve been thinking back to when I first decided to try for the amateur licence, back in 1965. I had always been interested in things radio and I recall, even back in the days of World War II, I had tried to make a transmitter using old 2V triode valves – quite unsuccessfully!

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The King Beckons My interest in radio continued but then I received a letter from the King, explaining that he would very much like my presence in his armed forces.

How could I refuse?

I enlisted and after a period of basic ‘square bashing’, I was told my trade in the R.A.F. would be as a Wireless Operator. During that time my interest in amateur radio became dormant, possibly because of the nature of my work.

On leaving the service in 1953, that interest reasserted itself, but then so did girls and radio once again took a back seat. I married in 1957 and some time later, whilst we were living in our flat in Worthing, my then boss, an ex-Army Radio Technician, loaned me his R1155 receiver and my interest in radio was reawakened.

Studying for the RAE Although I had been an R.A.F W.O.P (Wireless Operator) for 14 months in Germany, listening to Czech, East German and Russian Morse, after leaving there my Morse code memory became quite slow. Therefore, I felt that I needed to get in some practice in order to pass the required examinations. To this end, I got hold of an ex-army receiver, part of a ‘Wireless Set 18’, built a power supply for it and undertook to have a listening session every evening. I listened to the plentiful commercial CW in the 6 to 9MHz band and it wasn’t long before my receiving speed was up to 20 words a minute.

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C Next came sending CW and I knew this would be a problem because during my R.A.F. service, my job in the signals unit I belonged to was to receive only so I didn’t need to touch a Morse key after I left Radio School.

At this point I should say that passing the Morse test was at that time the last thing for me to complete because I had already passed the RAE at Chichester College.

So that I could improve my Morse code sending, I then built a CW oscillator and practised with it until I got my Morse sending speed up to 12 words a minute, the required test speed then.

For me, the CW testing station for aspiring amateurs was the Post Office building in Southampton, which I duly attended and much to my surprise, I passed the test.

Unnecessary Work!

Some two or so years later, I came across an official document showing that certain members of the armed forces had exemption from either the Radio Amateurs Examination, the Morse test or both.

To my chagrin, I found that an ex-R.A.F Wireless Operator had total exemption from both the RAE and the Morse test! All the time and effort I’d put into getting my Morse receiving and sending up to speed had been unnecessary. At least, it was good practice.

Finally I’d like to end by leaving you with the hope that the Club will again inspire a greater attendance so that we again might reach dizzy heights in competitions, contests, Field Days and so on.

A belated very happy New Year to you all.

73, Chris G3UFS

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CHAIRMAN’S CHATTER ’d like start by wishing all WADARC members a Happy, Healthy and Prosperous New Year for 2020 and beyond. It’s been a while since I last wrote in Ragchew and obviously some things have changed for WADARC and some, unfortunately, haven’t!

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TS Vanguard On the positive side, we’ve now developed a good relationship with the Worthing Sea Cadets and we have been able to use TS Vanguard for our meetings on a regular basis.

We’ve been able to remove unwanted items from the shack and we even made a profit from selling them for the Sea Cadets. The operating positions have now been separated and secured with new Tambour doors (roller shutters). The lock plates will be fitted very soon and then we’ll be able to securely install some of our radios.

Possible New Radio System The Club is currently in a good position financially and one of the things we’re considering investing in is new a Flex radio system that licensed WADARC members will be able to use remotely on non-Club meeting days. As well as HF, we also want it to cater for 4m operating as well as 2m and 70cms and for digital modes too.

Meetings We’ve altered the weekly meeting events schedule on our website so that there is a ‘placeholder’ for each meeting, especially when we’re not sure what the subject matter will be until almost the day itself. We have a few talks lined up and one or two suggested visits, but we do need people who are willing to give a talk or demonstration, even for half an hour. Although we prefer the subject to be loosely radio related, it doesn’t have to be.

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C Thanks The Club successfully set up and ran the usual special event stations in 2019 and we’re looking forward to repeats (or is that re-Petes) of them in 2020. My thanks to all who took part last year.

Committee meetings have been regular and productive and special thanks are due to Roger G7VBR for allowing us to use his QTH for them.

Still to Do On the negative side, we haven’t replaced any antennas at TS Vanguard yet nor have we installed any new ones. One issue has been a leaky roof there and nothing can be placed on the flat roof until it’s been repaired.

Unfortunately, with the best will in the world, some of the offers of help with erecting the antennas have not been forthcoming for various reasons so we are going to engage a professional aerial installer to do the work early this year. This will also overcome any issues with insurance for work on the building, which is important because it doesn’t belong to us.

Training to Return Membership figures are very slightly up but we still need more members if we are to survive as an interactive club. Please contact anyone you know who might be interested in joining, especially those who are thinking about obtaining a licence. They will soon be able to take part in our new training programme, which Kelvan M0KEL and Rod M0RDV are working on right now. We would also be pleased to welcome back past members.

I hope to see YOU at TS Vanguard.

73, Alan G4GNX

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SPECIAL EVENT STATION GB2WFB – WORTHING FIRE BRIGADE SES Edmund M0MNG reports on GB2WFB, the annual special event station the Club sets up at the Worthing Fire Brigade’s Open Day.

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arrived at the Worthing Fire Brigade station at around 0830 on the Saturday morning to find our antenna was already aloft and our tent was in place. I had wondered if the antenna might need to be put up on the morning itself because lightning had been forecast for the previous evening. In the event, none had materialised and Pete G4LKW got the antenna in the air on the Friday evening.

As usual our trapped dipole was supported by a tall tree at one end and it was tied off against the training tower at the other. Our tent and antenna are always in exactly the same position year after year!

We were ready to go on the air when the event opened to the public at 1000. Apart from a brief problem initially where our laptop refused to talk to our Icom IC-7300, the event passed off without a hitch.

This made a welcome change from 2018, when we suffered from overnight vandalism to the tent, problems with the mains power supply, the antenna falling down on the Friday night and some uncomfortably high temperatures.

This year, although conditions inside the tent became warm whenever the sun came out from behind some quite thick clouds, mercifully, the heat and humidity were nowhere near on the scale of 2018 and Roger G7VBR did not need to remove the back of the tent this time!

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C On the Air All but one of our HF QSOs were on 40m. The exception was AO50MOON on 20m, which seemed fitting because GB2WFB took place on the 50th anniversary weekend of the Moon landings.

Other special event stations included GB50WAB, which celebrated 50 years of Worked All Britain throughout 2019, which meant this was our one and only opportunity to get them in the log.

GB2WFB was also active on 70cms through the Club’s repeater GB3WO, using 1W from a Wouxun KG-UV6D. The two operators behind our most distant contact and our nearest contact on the repeater (West Chiltington and a military vehicle display on Broadwater Green respectively) turned out to be brothers. It’s an amazingly small world sometimes!

The final tally was 53 QSOs on 40m, 7 through GB3WO and the one on 20m from Spain which ended up being our best DX of the lot.

Band conditions were roughly comparable with the previous year.

There always seems to be QSB on 40m these days but I have heard much worse. Despite the low frequency, some of the fading sounded distinctly like Sporadic E.

Visitors We were visited by several local amateurs – Alan M6WHH, G3SPN from Worthing (not currently active) and the amateur from West Chiltington are the ones I remember. Apologies to anybody I have forgotten and especially to our friend from West Chiltington whose name and callsign have both slipped my mind!

The event was well attended rather than crowded and many of the passers-by had the opportunity to see amateur radio in action.

Thanks As ever, thank you to Pete G4LKW, Pete 2E0FVL and Roger G7VBR for being the driving forces behind this event.

73, Edmund M0MNG

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CORRESPONDENCE Jonathan G1EXG wrote in with his thoughts on whether it is better to fit a square tube into a round one or a round tube into a square one.

A Round Peg (Tube) in a Square Hole (Tube)

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was looking at a heavy square cross-section steel tube tail fixing on a truck the other day. In use, a slightly smaller size square tube slides into it so you can fix things like a trailer to the back of the truck.

In this particular case, the truck owner was a radio amateur and he used the heavy fitting to support a 'guy wire free' mast for his antennas when out portable.

I was looking at this and thinking how it's not always easy to get the correct square cross section tube because round tubes are more common. However, the thick square tube could take a round tube, as long as it was bolted properly and was a good snug fit, of course.

In the past I have resorted to using short lengths of round tube to connect two square booms for long antennas (when I could not find the correct square tube to do the job).

Sometimes I have actually found the correct square tube only to discover it's made of steel instead of aluminium and then I've been disinclined to use it because it's never a good idea to mix metals (electrochemistry causes premature corrosion).

Which is Best?

All this got me thinking, which would be the best fit: i) a round tube slotted snugly into a square tube or ii) a square tube slotted snugly into a round tube?

If we assume the tubes are thin (or we use the inside dimensions of the outer tube and the outer dimensions of the inner tube), we can work out the cross sectional areas of the various tubes to calculate their ratios to determine which is the best and worst fit.

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i) ROUND TUBE INSIDE A SQUARE TUBE (Fig. 1) Area of outer square tube = (2r)2 = 4r2 Area of inner round tube = πr2 Therefore, the ratio is πr2/4r2 = π/4 = 0.79 This means the round tube fills 79% of the available inside area of the square tube. ii) SQUARE TUBE INSIDE A ROUND TUBE (Fig. 2) Applying Pythagoras, we get a = R/√2 giving the area of the inner square tube (2a)2 = (2R/√2)2 = 2R2 Area of the outer round tube = πR2 Therefore, the ratio is 2R2/πR2 = 2/π = 0.64 This means a square tube fills only 64% of the available space inside a round tube.

So, I am sure you are relieved to know (perhaps you intuitively knew?) we have our answer: It seems that a good fitting round tube in a square hole is better than a good fitting square tube in a round hole!

73, Jonathan G1EXG

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DAYTON HAMVENTION Pete G0TLU always wanted to go to the famed amateur radio rally in Dayton and last year he made it. As it was his first visit to America, he went with his wife and turned it into an epic trip right across the country.

First Visit to the Dayton Hamvention

Chicago

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t has long been my ambition to visit the USA generally and the Dayton Hamvention in particular. The opportunity eventually arose last year when I took voluntary redundancy/early retirement and then I finally had enough money to make it a reality.

To help with planning our trip, I sought the advice of Roger G4TNT because he is a regular visitor to both the USA and the rally. We decided to fly into Chicago as it’s not too far from the show and because my XYL Margie has some distant relatives there. This gave us an address to put on our ESTA application before we’d booked any accommodation. Most British citizens don’t need a visa to travel to America but they do need an ESTA and you won't get in unless you obtain one before you go.

Our application was approved within a couple of days and we headed to Trailfinders to make the arrangements. Roger had given us many suggestions and pointers so we had a good idea of where we wanted to go but as we needed to book flights, car hire and some of our accommodation, we found using a travel agent was a great help. After Dayton we wanted to travel to the West Coast and the agent suggested

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C that we take a train instead of flying so we would see the country we were passing through. This turned out to be an excellent idea and comparable in price to taking a plane.

Chicago Once we arrived in Chicago, we visited as many of the tourist attractions as we could – the Willis (formerly Sears) Tower where you can step out into the Sky Deck, a box made completely of glass on the 103rd floor (see photo), and then the John Hancock Tower, which has 'The Tilt', a contraption you step into and it then tips you out over the landscape at an angle of 30 degrees. We also took in Navy Pier, a boat trip on Lake Michigan, the Magnificent Mile shopping area and many other attractions. We treated ourselves to the famous Chicago pizza on more than one occasion too!

XYL Margie in the Sky Deck

On to Dayton After five days we picked up our first hire car for the trip down to Dayton.

Although it was only about an inch on the map, it’s actually the best part of 500 miles and the journey took us a whole day. It wasn’t a problem because I found driving in the States surprisingly easy to get used to and the standard of driving was somewhat better than here! However, I noticed some of the major roads were in a disappointingly poor condition.

On arriving at our hotel in Miamisburg, a few miles from Dayton, we were impressed by the value for money. It was a very nice suite for the price we paid.

We headed to the rally early the next morning and found Roger relaxing on a bench in the middle of the action, having already 'done' much of the rally the previous day while we were still on the road. We also bumped into Ed M0MNG, who was with the ICQ Podcast gang, and Phil G4UDU. The sheer scale of the event is mind-boggling, taking up acres of land, three huge hangar-like buildings and several smaller ones. That's without the outdoor flea market, which was bigger than any I've ever seen. I later bumped into Ed again while he was operating the rally Special Event

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C Station on 40m. When I arrived at the Elecraft stand to buy a case for my KX2, I joked with the staff that I had to come over to Dayton to get one as Waters & Stanton didn't have any in stock!

The whole event was extremely well organised, with an app to guide you so you could find your way around and to help you meet up with others. There were plenty of cheerful volunteers driving golf carts to help the less mobile or the just plain tired to get around the site and to and from the car parks.

There was also huge support from the local Sheriff's Department both on and off the site and the Sheriff and his men had their own carts too to patrol the site, some equipped with the obligatory blue and red lights.

In the evening we met up with Roger again and visited the Dayton Amateur Radio Association (DARA) clubhouse, which has HF and VHF shacks, meeting and dining areas, an impressive collection of towers and antennas and is home to several repeaters.

The next day we visited the nearby US Air Force Museum, which had examples of everything from airships and the Wright brothers' early machines to the latest 'stealth' Just some of the DARA antennas aircraft.

Amtrak Time After Hamvention we returned to Chicago and visited the relatives, who fed us very well and showed us some more of the sights. It was then time to return the hire car and take a taxi to the rail terminal to board our train, the Amtrak Southwest Chief, which would be our home and transport for the next three days. We had a compact but comfortable cabin with bunk beds, which became a comfortable double seat during the day, and even a shower and loo. We spent a lot of time in the observation car with a drink or a cup of coffee, watching the scenery gradually change from endless flat plains to dramatic mountains as we headed West. It really is a very civilised way to travel.

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C LA Arriving in Los Angeles, we picked up our second hire car. We were now in the phase where we had no accommodation arranged because we wanted to be as flexible as possible. We found a very nice (and expensive!) hotel in Long Beach, in sight of the Queen Mary. I later found out it was particularly expensive because it was the Memorial Day holiday weekend and almost all hotels put up their prices then.

Arizona Next we headed into Arizona. I particularly wanted to visit the Titan Missile Museum (TMM) near Tucson and operate from there using the 80-foot tall HF discone antenna left over from when the site was operational during the Cold War. This has been adopted and maintained by local Green Valley ARC and there are several YouTube videos showing amateurs operating through it.

When we arrived there, we first toured the museum, which is a decommissioned ICBM launch site, with its underground control room that is mounted on huge springs to withstand the vibration of the missile taking Titan ICBM missile off, then were led through an underground walkway to the missile silo itself. There we saw the awesome weapon which would have been fitted with a ninemegaton warhead, sufficient, we were informed, to destroy a city the size of Los Angeles. The missile was propelled by a two-part fuel and, once mixed, the missile could not be stopped from taking off.

The guide, who had served on the base before its closure, explained that the personnel were not told Do NOT touch that button! their target but they did know that the warhead was configured as 'ground burst' so they believed its destination would have been a hardened target, such as an enemy missile site. After launch, the base personnel's orders were to remain underground for two weeks before emerging to see what was left of the USA and decide for themselves what to do from there!

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C On the Air After the silo tour, I signed the logbook in reception and headed out to the car park and a picnic table just the other side of the fence from the HF discone to operate as W7/G0TLU. The Green Valley ARC has installed a metal box next to the table, which you open and unroll the coax inside. This was terminated in a PL259 and, luckily, I had remembered to take an adaptor to connect this to my KX2's BNC socket.

The discone is said to have a reasonably low SWR across HF and the auto-ATU in the KX2 quickly got a 1:1 match on all bands. A greater concern was keeping a wary eye out for the rattlesnakes the museum staff had warned us were about.

Seeing or, even worse, hearing one of those would have done my CW sending no good at all!

Conditions were not great and, of course, a discone has no gain so I was quite pleased with a 449 report on 20m from AB0BM in Cherokee, Iowa, a good thousand miles away.

Later I was pleased to see I had RBN spots from quite a few US stations as well as one in Canada, although reported signal strengths were on the low side (I did crank the rig up to its maximum 10W after fruitless CQs on 5W).

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C Grand Canyon Next, we headed up to the Grand Canyon.

We've all seen pictures of it , but until you see it in real life, it's hard to appreciate the sheer scale of it. From the visitor centre, you walk up a gentle incline and then suddenly there it is laid out before you – totally breathtaking!

Monument Valley From there we headed north to the iconic Monument Valley. We arrived just in time to see it being lit by the evening sun. It was another breathtaking sight.

Finally Then it was into Nevada and Las Vegas for our flight home. I was amused to see there were fruit machines even in the departure lounge at the airport there.

All in all, our 'Holiday of a Lifetime' surpassed all our expectations and I hope to be able to visit the USA again one day, including the Dayton Hamvention, of course.

Now, I’m wondering if my new employer is planning any voluntary redundancies?

73, Pete G0TLU

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G1EXG’S SHORT CIRCUITS This time Jonathan G1EXG looks at variable and vacuum capacitors and explains how they’re used in amateur radio.

SHORT CIRCUIT NO. 22: VARIABLE CAPACITORS & VACUUM CAPACITORS

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capacitor is a device consisting of two or more metal plates separated by air or another insulator (see a previous Short Circuit for more information).

A tuned circuit needs an inductor and a capacitor. In a radio receiver circuit or filter, the inductor can be an air cored coil or have a ferrite core (to increase the inductance) while the capacitor can be one of a number of fixed types (e.g. ceramic, polystyrene and so on) or a variable (e.g. ceramic, Jackson, beehive types and so on) one.

Tuned Circuit The resonant frequency of a tuned circuit is given by: f = 1/π2√(LC) Therefore, either the inductance or the capacitance can be varied to adjust the resonant frequency of the circuit. If you decide to use a variable capacitor, its vanes can move, allowing the capacitance to be varied.

However, because the capacitance part of the resonance is dependent on 1/√C, as you turned the capacitor to tune, you could easily get a very non-linear spacing of stations across the dial (for example, all bunched up at one end). You can shape the capacitor vanes so as you turn the shaft it accommodates for this 1/√C effect. I expect that's why many variable caps don't have simple round vanes or the shaft is offset from the middle.

Example 1 – A 2m Band ZL Special Some antennas require a capacitor to balance the reactance of the design. For example, a 2m band ZL special Yagi antenna needs a small amount of extra capacitance across the feed point to produce a good match. We can estimate the typical voltages present on the capacitor from: power P = V2/R, so V = √(P x R). Which for 50W power into 50Ω gives V = √(50 x 50) = 50V across the capacitor. So an air spaced beehive variable capacitor will work well and be stable in this application because the voltages are fairly low (as long as the matching to 50Ω stays good).

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C The beehive capacitor is fabricated from several air spaced concentric cylinders that intermesh to a create a 'useful' capacitance in a relatively small volume. In use, you turn the top of the beehive trimmer which screws down on a thread, thus increasing the overlap between the two sets of concentric plates and increasing the capacitance.

A typical large air spaced capacitor and a vacuum capacitor (pen for size comparison)

Example 2 – A Small Transmitting Loop A small loop antenna (that is, small in terms of wavelength) can consist of a ca. 1m diameter loop brought into resonance using a large capacitor.

The loop must be made of a relatively large cross section diameter (e.g.

2-3cm) good conductivity metal tube (such as aluminium or, better still, copper). The capacitor has to have a very low resistance connection to the loop and be heavily built with wide spacing between the plates. The

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C result is a very high Q resonant circuit. As a result, very high currents (loop) and voltages (capacitor) exist on these components even with fairly modest powers. Therefore, 50W transmitted via a loop will create far higher currents and voltages than on the ZL special.

Capacitor Choice The capacitor may well have thousands of volts peak so it’s apparent you can't use a small beehive cap in this application (although it would work fine for receive only). You have to scale-up a variable capacitor so it can handle the voltages.

In addition, it should be remembered that if the voltage is large enough, a spark can jump across an air gap because a sufficiently high voltage breaks down (ionises and then conducts) the air.

If you want an air spaced capacitor to cope with high voltages, the plates need to be far apart (that is, several millimetres rather than the fraction of a millimetre normally found in a typical tuning capacitor).

Unfortunately, the capacitance drops inversely with the plate spacing and this is why useful high voltage capacitors end up being fairly large and chunky!

Vacuum Capacitors A way around this problem is to pump the air out of the capacitor. These so-called vacuum capacitors can take much higher voltages than an air space capacitor of the same spacing because there is no air between the plates to break down, only the outside glass cover. They are often similar in construction to a giant beehive capacitor.

Another advantage of a vacuum capacitor is that because it is inside an evacuated glass container, it will remain very clean. This is unlike an air space capacitor which, over time, become oxidised and dirty, leading to a loss in performance.

73, Jonathan G1EXG

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BOOK REVIEW

by Jonathan Hare G1EXG

Science and technology such as radio have not been uniformly well represented or portrayed in films and novels. I think All the Light We Cannot See, a novel by Anthony Doerr, is different and I believe a lot of radio amateurs would enjoy reading it.

This novel is not only wonderful storytelling but it also manages to convey some of joy and a sense of wonder and discovery many of us will relate to as radio amateurs. In this WW2 based story a German boy, Werner Pfennig, saves himself from an impoverished and claustrophobic life down in the mines through his own industrious experiments and hands-on experience exploring radio.

At one point the young Werner is out in the woods using directional finding radio equipment that he has designed and built himself: "... Werner sets up the first transceiver, uses measuring tape to pace off two hundred meter, and sets up the second. He uncoils the grounding wires, raises the aerial, and switches them on. Already his fingers are numb.

"Try eighty meter, Pfennig. Typically teams won't know what band to search. But for tonight, our first test, we'll cheat a bit."

An 80m band quote is not something you often read in a novel but it is the kind of everyday comment that a radio amateur would be familiar with. The book is not only a riveting story, it also manages that very difficult balancing act of keeping the science and technology pretty realistic during the telling of a moving and powerful story.

All the Light We Cannot See by Anthony Doerr Published by 4th Estate Harper Collins, 2014, ISBN 9 780008 138301

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RALLIES FEBRUARY 1st – Barry ARS Tabletop Rally The Wilton Lounge, Sully Sports & Leisure Club, South Road, Sully CF64 5SP 2nd – South Essex ARS Canvey Radio & Electronics Rally Cornelius Vermuyden School, Dinant Avenue, Canvey Island SS8 9QS 7-9th – Orlando Hamcation Central Florida Fairgrounds and Expo Park, Florida USA 9th – Harwell Radio and Electronics Rally Didcot Leisure Centre, Mereland Road, Didcot OX11 8AY 15th – Ballymena ARC Rally Ahoghill Community Centre, 80 Cullybackey Road, Ahoghill BT42 1LA 16th – Radioactive Rally Nantwich Civic Hall, Cheshire, CW5 5DG 16th – Lomond Radio Club Bring-N-Buy Event Lomond Radio Club Bring-N-Buy Event 23rd – Rainham Radio Rally The Victory Academy, Magpie Hall Road, Chatham, Kent, ME4 5JB 23rd – Red Rose Winter Rally St Joseph’s Hall, Chapel Street, Leigh WN7 2PQ MARCH 1st – Exeter Radio & Electronics Rally America Hall, De la Rue Way, Pinhoe, Exeter EX4 8PW 8th – Pencoed ARC Tabletop Sale Pencoed Rugby Club The Verlands, Felindre Road Pencoed CF35 5PB 15th – Wythall Radio Club Hamfest Club HQ, Wythall House, Silver Street, Wythall B47 6LZ 29th – Dover ARC Hamzilla Radio Fest & Electronics Fair Discovery Science Park, Ramsgate Road, Sandwich CT13 9FF 29th – Callington Radio Rally Callington Town Hall, Callington, Cornwall PL17 7BD

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